Hello
I recently bought a used TDS 380 that is for the most part functional with the exception of some issues with the vertical scale and dc/ac coupling, I have attachments to show you what I mean. This is my first oscilliscope by the way.
Basically what is going on is the vertical scale seems to have group of bad spots affecting both channels, the the input signal seems to distort and drop out. When I roll the vertical scale past this bad section, either lower or higher, everything works fine again. In fact I don't know why I get a calibration error message because both channels seem to be measuring accurately. And to add, the dc coupling for channel 2 doesn't seem to work, I get a flat trace with either a ac or dc signal applied. If I apply enough ac signal into ch 2 on dc, I start to get a signal but a distorted one. Other than these issues I have, everything seems to work perfectly fine.
I am wondering if maybe I have a bad hybrid, maybe changing the capacitors will help, or perhaps I have bad chips on the main board which I am hoping not! What do you think is going on?
tds380_1 This is the scope itself
tds380_2 When I power on the scope all the lights come on as normal and I hear relays clicking
tds380_3 Every time this scope powers up I get this screen, calibration fail but at least power up passes
tds380_4 I take at the calibration screen to notice the signal path failed but all other tests passed
tds380_5 Taking a look at the error log I see calibration error relative amp gain, what does that mean? Also the memory read error is from the floppy drive
tds380_6 Both channels show normal traces with no sources connected
tds380_7 Both channels connected to the 5V probe pin, no problems here
tds380_8 Both channels seem to work fine on ac coupling
tds380_9 With both channels on dc coupling, ch 2 seems to have a dc coupling problem
tds380_10 Here I am feeding both channels a 1kHz square wave output from a sound card in the good portion of the vertical scale, everything is fine
tds380_11 When I adjust the vertical scale to the group of of bad settings, both channels seem to slightly drop out and show distortion
tds380_12 and tds380_13 With the vertical scale set in the bad region and both channels connected to 5V probe pin, we again see abnormal results (both channels ac coupling)